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Backspacing for asi1600mm pro + WO z61

Astrophotography CMOS
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#1 shrimpus

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Posted 01 March 2021 - 08:38 AM

I just ordered a zwo asi 1600mm pro kit, and i was wondering what I should set my flat61 at to meet the backspacing requirements? I have it set at 12.9 for my dslr, but it’s obviously going to be different with the new camera.

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#2 Jim Thommes

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Posted 01 March 2021 - 02:40 PM

DSLR is usually 44 mm with T-ring. You added12.9 mm spacing to your flat61 for a total of 56.9 mm. If you are happy with what you are getting with the DSLR, you can work with this information.

 

 ASI1600m has 6.5 mm back focus with the 11 mm female to female ring removed (which you do to attach the FW). The filter wheel is about 19 mm, so this ASI1600 kit has a total of 25.5 mm. From your DSLR set up, you were happy with 56.9 mm, so a good starting point for a spacer would be 31.4 mm. This seems about right since the ASI1600m kit does have a pretty short back focus.

 

Caveats are that depending on your filters, you may need to reduce the back focus calculated for the camera and FW and as such, you may need a little more than an additional 31.4 mm. Might be real convenient to start with a standard 30 mm spacer and add shims as needed.


Edited by Jim Thommes, 01 March 2021 - 02:43 PM.



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